Radio receiver



March 26, 1940. H. GAYSON 2,195,301

RADIO RECEIVER Filed May 18, 1939 #WOR/VIV 'Patented Mar. 26, 1940 UNITED STATE s PATENT y OFFICE RADIO nEoEivER Harry Grayson, London, England, assigner to Baird Television Limited, London, England, a

British Company Application May 1s, 1939, serial No. 274,354

In Great Britain December 12, 1938 2 claims. .(01. 25o-9.9)l

when the receiver is required to operate on va waveband other than that to which the aerial connected to the said feeder is appropriate.

According to the present invention there is provided a radio receiver. adapted to be fedwith signals from a twin or coaxial feeder in whichv the earthy point of said feeder is connected to earth and to the grid circuit of a valve of the receiver through condensers.

In order that the present invention may be more particularly described reference` is now vmade to the accompanying diagrammatic drawing which illustrates by'way of lexample partv of a radio receiver according lto the present invention.

In the drawing a dipole aerial I is connected by means of a balanced feeder 2 to an inductance 3 kin the receiver.- The inductance 3 has its centre point returned to the earth line through a condenser 4 and this point is also connected through a further condenser 5 and a tuned cir? cuit 6 to the grid of a valve 'I. The grid of the valve I is returned to the earth line through a lresistance 8. Coils 9'and I0 are arranged to be connected between -the grid of the valve I and earth by means of switches IIv and I2..

The operation of the circuit is as follows. When the switches II-and I2 are open signals received on the dipole I are fed through the coil 3 to the tuned circuit 6 and thus applied to the grid of the valve 1, the condensers 4` and 5 being such that theyoffer. a low impedance at the frequency to which the circuit 6 is tuned.`

- wave-lengths between 200 and 500 metres.

When either ofthe switches II or I2vis closed `the appropriate coil 9 or I0 is tuned by condensers 4 and 5 in series to a frequency at which the inductance of the tuned circuit 6 is negligible.`

When a shielded twin or a coaxial feeder is employed, the outer or shielding conductor is connected to the junction of the condensers 4 and 5.

The present invention is especially applicable to receivers adapted to receive signals in the television waveband as well as a number.y of preselected stations in the broadcast band. In this case the dip'olel and' tuned circuit 6 are tuned to .the television waveband while the coilsA 9 and I0 are such as tok be tuned by the condensers 4 and 5to 'frequencies in the broadcast waveband. For example, the valve 1 may be adapted to lamplify both sound and vision frequencies in a television system; the aerial I` and tuned circuit 6 being arranged to resonate at say 45 -megacycles.v The shunt capacity of the tuned circuit 6 may in this case be thestray circuit capacity and the input capacity'of the valve 'I. The condenser 4 would in this case be some -200 micrornicrofarads` while the condenser 5 would be adjustable and of the 'order` of 100 micromicrofarads. The inductances 9 and I0 are preferably made variable and such as to be tuned Aby, the condensers 4 and 5 in series to It is also'desirable to shunt the tuned circuit 6 by a resistance I3 in order to flatten its response curve sufciently to coverl the wide frequency y band necessary for television reception.

Itis, of course, possible otherwise to vary the circuit arrangement shown. 'o

I claim: t o 1. A radio receiver arranged to be fed with high frequency signals from a twin or coaxial feeder comprising .a valve having ,a grid circuit, means including condensers for connecting the earthy point Aof said feeder to earth and to said grid circuit, a first inductance arranged to be supplied with high frequency signals from said feeder, a second inductance inductively coupled with said first inductanceA and connectedv at one end to said grid circuit and at the other end through said condensers to earth,` means in shunt therewith for tuning said second inductance t0 said highfrequency, atleast a third inductance, and means yfor selectively connecting said third inductance between the grid circuit and earth.

2. A vradioreceiver according to claim 1 and in which a fourth inductance is provided with HARRY GRAYSON.

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